This invention relates generally to package wrapping machines utilizing thin, stretchable film to wrap and display articles contained in trays and, more particularly, to apparatus for improved handling of the trayed articles within a wrapping machine.
A variety of film wrapping machines are known in the prior art for wrapping articles, for example, agricultural commodities, supported on trays. Typically, a trayed commodity is transported on a conveying platform to a wrapping station where film if wrapped about the commodity oftentimes with the film being folded under the tray and sealed therebeneath to form a display package. In one popular form of wrapping machine, the wrapping station comprises an elevator having collapsible slats spring-biased to a vertical position for supporting the trayed commodity on the upper surface of the vertically extended slats. In this form of machine, the elevator is raised to elevate a trayed commodity into engagement with a sheet of film which is thereafter folder under the tray with the underfolding apparatus collapsing the slats of the elevator against the spring forces.
As a trayed commodity is transported to the wrapping station, the trayed commodity contacts a package stop so that the conveying platform can be moved out from under the tray to leave the trayed commodity correctly positioned at the wrapping station for the wrapping procedure. In modern high speed wrapping machines which transport trayed commodities at relatively high speeds, the contacts with the stop are often quite sharp and can be more accurately termed collisions. These collisions of trayed commodities with the package stop potentially can create considerable reaction forces. However, until recently, almost all operators of such wrapping machines utilized commodity supporting trays which were formed from a variety of plastic foams or pressed fiber. When such trays strike the package stop to deposit the trayed commodities at the wrapping station, the force of the collision is absorbed by the foam or the fiber such that little reaction force is exerted to tend to move the trayed commodity away from the stop.
In what may be a growing trend, a number of local and state regulations have been passed to require a "see-through" tray so that the consumer can view the underside of the package. Such see-through trays, for example, prevent packages from concealing less attractive portions of a commodity beneath attractive portions which show through the film on the top of the package.
While one form of acceptable see-through tray is formed by a lattice work of pressed fiber, a growing number of packagers required to use see-through trays are utilizing a clear plastic tray which has considerable resiliency. Unfortunately, when such a tray is used and the commodity adheres to the tray, considerable reaction forces can be generated by the collision of the trayed commodity with the package stop.
Commodities supported on such resilient plastic trays tend to bounce away from the stop due to the reaction forces and, hence, may be displaced from a correct position for properly wrapping the trayed commodity. At best, packages positioned away from the correct position at the wrapping station are not optimally wrapped and at worst, such packages are positioned such that they jam with a portion of the wrapping machine or indeed are entirely ejected from the wrapping machine. The trayed commodity can be displaced from the stop either longitudinally (toward the package entrance direction), laterally (to one side or the other) or diagonally (at an angle) with the exact displacement depending upon the longitudinal and lateral components of the reaction forces generated by the collision of the trayed commodity with the package stop.
Opaque plastic trays similar in design and resiliency to the clear plastic trays are also being introduced by some tray manufacturers and may make the package displacement problem more widespread within the industry.
Thus, it is apparent that the need exists for an improved package handling system for film wrapping machines when commodities are supported on resilient trays capable of generating substantial reaction forces upon contact with a package stop.